Overview and comparative study of two control strategies used in 3-phase grid-connected inverters for renewable systems

摘要

In this paper, an overview of grid-connected renewable systems is presented, then two current-control strategies for 3-phase grid-connected inverters are analyzed: firstly, the well-known d-q control in the rotating synchronous reference frame (d-q axes) using Proportional Integral regulators is described, and secondly, the Proportional Resonant controller in the Stationary Reference Frame (αβ axes). In order to obtain a high efficiency of the system when the 3-phase utility grid voltages are affected by harmonic pollution, a Harmonic Compensator (HC) structure is used with the Proportional Resonant controller, this due to the ease way to compensate harmonics when a Proportional Resonant control is utilized instead of a d-q control. Then both control strategies (d-q control and PR + HC) are analyzed under harmonic pollution condition. For both strategies, a Positive Sequence Detector plus a Synchronous Reference Frame Phase-Look Loop (PSD + dqPLL) is used as the synchronization algorithm. After the study, it was observed that the PR controller provides a greater facility for carrying out the harmonic compensation process helping to fulfill with the international standards. A model of a grid-connected photovoltaic system with a nominal power of 10 kW is used to evaluate and compare the performance of the current-control strategies. For this, a Real-Time Digital Simulator (RTDS) platform is used.